Chaz replied:

Hi Conman,
Yes it is possible to tighten a "clutch type" LSD. I use to do it to the ford 9 inch diffs for drag racing, simply by adding an extra shim to the clutch pack. Of course this would be detrimental to a street car, in that it wouldn’t allow the differential action during cornering and this would be hard on tyres and axels. If your going to all the trouble of stripping the diff down, then you may as well replace the clutches and springs with heavy duty ones to reduce the slip. If your after anything more then perhaps a auto locker would be a better option.
Good Luck
Chaz

Phil G replied:

An oil change sometimes makes an LSD work better. Also Penrite sell an additive that enhances LSDs.

Truckster (Vic) replied:

Yes it can be done, and its about $200-300 depending who and where does it.

Bundyman replied:

Conman the cheapest way to tighten up your LSD is to fill it with normal diff oil. I filled a LSD on a rodeo with normal diff oil and it chirped all day long on the bitumen. I had to add a "friction modifyer" to ease up the tyre wear. This might be the cheapest way but in the long run you will end up stuffing your LSD - but this might give you enough time to save up for a diff locker.

Cheers,
Hughesy